ExVSK, the only thing you can do, unfortunately, is to keep disputing.
If you post videos that are shorter than 15 minutes, you won't get hit
as hard. I know it sucks to have your hand forced, but it's a way to
keep them from getting what they want: you quitting, or joining them. I say you do that
walkthrough of B:AC when it comes out. Post loads of 15 minute videos.
Make sure that they understand that you won't be pushed around. If they
hit you with a copyright claim, you dispute and upload another video.
keep disputing. Keep posting comments. Email admins here, and contact
the publishers of the games you do LP's of. Most of them are very happy
that people make these kinds of videos, and the rest don't really care,
so there is nothing to worry about from them.
Sooner or later, something is bound to happen. We'll just have to hope that it's sooner.